Reactive Liquids for Non–Prestonian Chemical Mechanical Polishing of Polysilicon Films

Abstract

Slurries which yield non-Prestonian polysilicon (poly-Si) removal rates (RRs) are desirable during the fabrication of semiconductor and microelectromechanical systems (MEMS) devices. Here, we show that aqueous solutions of 250 ppm poly(diallyldimethylammonium chloride) (PDADMAC), DADMAC (monomer of PDADMAC) or guanidine carbonate (GC) at pH 10 give high poly-Si polish rates. Addition of 25 ppm cetylpyridinium bromide (CPB), a cationic surfactant to any of these solutions modifies their polish performance to non-Prestonain behavior. The underlying mechanism for the non-Prestonain removal of poly-Si films with the RL containing 250 ppm PDADMAC + 25 ppm CPB solution at pH 10, chosen as the model system, was investigated using ultraviolet-visible (UV-Vis) spectroscopy, zeta potential measurements and fourier transform infrared (FTIR) spectroscopy. These analyses suggest that CPB adsorbs strongly on poly-Si and suppresses RR at 1 and 1.5 psi to ∼0 nm/min. At higher pressures, the binding between CPB and poly-Si is ruptured due to pressure applied by the polishing pad during CMP process allowing the nitrogen atom of PDADMAC to access and bind to the negative dipole of underlying polarized -Si-Si- bonds. The polarized and weakened backbone Si-Si bonds are broken during polishing, yielding high RRs.